1. Field of the Invention
The present invention relates to a procedure for controlling an elevator group. More specifically, the present invention relates to controlling an elevator group including at least two double-deck elevators such that the best deck of each elevator serves a landing call to optimize passenger journey time.
2. Background of the invention
When a number of elevators form an elevator group that serves passengers arriving in the same lobby, the elevators are controlled by a common group controller. The group control system determines which elevator will serve a given landing call waiting to be served. The practical implementation of group control depends on how many elevators the group includes and how the effects of different factors are weighted. Group control can be designed to optimize cost functions, which include considering e.g. the passenger waiting time, the number of departures of the elevators, the passenger ride time, the passenger journey time or combinations of these with different weighting of the various factors. The group control also defines the type of control policy to be followed by the elevator group.
Additional features will be added to group control when the elevators are double-deckers, where two decks are attached on top of each other in a frame and the elevator serves two building floors simultaneously when the elevator stops.
A conventional control solution is based on collective control, in which the elevator always stops to serve the nearest landing call in the drive direction. If the call is allocated to the trailing car, coincidences with possible landing calls from the next floor are maximized. Collective control in elevators with normal cars is ineffective in outgoing and mixed traffic. The consequence is bunching and bad service for the lowest floors. The same applies to collective control of double-deck elevators. For example, U.S. Pat. No. 4,632,224 presents a collective control system for double-deck elevators in which a landing call is allocated to the trailing car in the travelling direction of the elevator. In other words, when the elevator is moving down, the landing call is allocated to the upper deck, and when the elevator is moving up, the landing call is allocated to the lower deck. Another U.S. Pat. No. 4,582,173 discloses a group control for a double deck elevator calculating internal costs corresponding to the waiting times inside the car during the stops and external costs corresponding to the waiting times on the landing call floors. In this control only the operating costs consisting of these time losses of the passengers are minimized.